The present invention broadly relates to pressure measurements and, more specifically, pertains to a new and improved construction of a pressure sensing device.
Generally speaking, the pressure sensing device of the present invention comprises a sensor for delivering an electrical output signal in response to a pressure and such contains a first chamber, a second chamber and a wall member separating the first chamber from the second chamber. The wall member is arranged to deflect under the influence of pressure in the first chamber. A leaf spring is arranged in the second chamber and has a fixed end and a free end. The leaf spring is fixedly mounted in the second chamber at the fixed end. The wall member has a middle region and is mechanically coupled at the middle region to the leaf spring. The free end of the leaf spring cooperates with a measurement transducer serving as a contactless transmission element.
A sensor or sensing device of this type serves for converting or transforming the physical phenomenon or variable of pressure into an electrical value. The output value of the sensor or sensing device is dependent upon pressure and can serve to control an electrical contact or can form an input value for a control or regulating device. Such a sensor or sensing device can, for instance, be employed in two-threshold or window-type regulation or for constant regulation. The sensor or sensing device can also serve as a simple signal transducer or generator.
A sensing device of this type is known from the U.S. Pat. No. 2,950,421, granted Aug. 23, 1960. One chamber of this known sensing device is under vacuum while the other chamber is formed as a pressure-sensitive diaphragm chamber within the vacuum chamber. The diaphragm chamber can be subjected to the pressure to be measured. A deflectable wall of the diaphragm chamber is connected to a leaf spring arranged in the vacuum chamber. The leaf spring forms the movable contact of a double-throw switch. Cable seals are required for conducting the connections of this switch out of the vacuum chamber. The movable contact of the switch forms a condensor or capacitor in relation to one of the fixed contacts. The air gap of this capacitor is variable due to the motion of the movable contact. The cable seals are a disadvantageous feature of this known sensing device, since they can cause leakage leading to a diminution or loss of the vacuum. This known sensing device is furthermore only suitable for measuring a pressure and not for measuring a differential pressure.
A measurement transducer for converting or transforming a pressure into an electrical value and having a contactless transmission element is known from the French Pat. No. 1,187,259, granted Mar. 2, 1959. This measurement transducer comprises an aperture or aperture-screen which modulates a light beam and serves as a contactless transmission element. The contactless transmission element is coupled by a plunger to a diaphragm exposed to the pressure to be measured. The plunger in this measurement transducer is conducted out through an opening to the transmission element, so that this chamber is connected with the ambient atmosphere through the opening. This known measurement transducer is therefore not suited for measuring a difference in pressure.
A pressure measuring apparatus comprising a measurement transducer with inductive sensing is known from the U.S. Pat. No. 2,260,837, granted Oct. 28, 1941. The transmission element of this measurement transducer is arranged between two coils. A U-shaped core is associated with each of the two coils. Transmission of the pressure to be measured from an accordion bellows to the transmission element is effected by means of a massive plunger which is centered by a diaphragm. To the extent that the pressure to be measured is taken up by the accordion bellows in this known sensor, the diaphragm serving to center the plunger causes supplementary frictional resistance which detrimentally affects the measurement accuracy in relation to fine pressure differences.
An apparatus for controlling the pressure of a fluid delivered by a pump is known from the British Published Patent Application No. 2,089,497, published June 23, 1982. A membrane-controlled transmission element in the form of a leaf spring supports a flag at its end for interrupting a light beam when the pressure of the fluid increases. The transmission element is located outside the pressure chamber in this known arrangement, as it is in the two previously mentioned patents, French Pat. No. 1,187,259 and U.S. Pat. No. 2,260,837.
A barometric pressure measurement diaphragm chamber is disclosed in the U.S. Pat. No. 3,451,272, granted June 24, 1969. The diaphragm chamber is arranged within a U-shaped curved spring. This device serves as a barometer for measuring the atmospheric air pressure and does not comprise any measurement transducer having a contactless transmission element.